There are many occasions where it is necessary to process and transmit color computer video signals. In one such instance, when analog VGA video and keyboard signals are routed between one of a plurality of computers and a single monitor and keyboard by switching equipment, such as the Commander.TM. module manufactured by Cybex Computer Products Corporation located in Huntsville, Ala., analog VGA video levels routed thereby may be reduced and high frequency components of the signal attenuated by switching circuitry inside the Commander.TM. module. Further, a problem often occurs as a result of interaction between the color signals.
In another instance, where analog video and other data signals are coupled to or between workstations via relatively long conductors, similar signal losses occur. In order to compensate for these signal losses, it is generally necessary to regenerate voltage amplitude of the video and data signals prior to inputting them to a monitor and other peripheral devices. Typically, such regeneration is done by a pair of transistors coupled in a common emitter configuration, with the first transistor inverting the signal and the second transistor reinverting the signal in order to provide non-inverted voltage amplification. While this type of amplifier requires power of a single polarity and ground, D.C. coupling of the amplifiers is generally difficult to implement and not particularly stable.
Accordingly, it is an object of this invention to provide video circuitry which is simple in construction and which possesses a voltage gain factor sufficient to boost a weak analog video signal to a conventional, usable amplitude.
Additionally, it is an object of this invention to provide a constant current, high frequency enhanced, video transmitter disposed to operate with a single polarity source of D.C. power with respect to ground. As a feature of the invention, the enhancement is achieved by a two-unit amplifier wherein an input of one unit is coupled through a generally like unit of the other unit and wherein coupling between the two units employs at least one reactance path which selectively lessens gain at certain relatively lower frequency ranges to thus relatively provide selected high frequency gain at, at least, one selected range of frequencies.
Further, it is an object of this invention to provide a communications system wherein a transmitter and receiver are located at substantial distances, and wherein an improved video transmitter is employed to feed a transmission line which is terminated by an enhanced video receiver, enabling relatively long cables to be employed between transmitters and receivers.
A further feature of this invention is to provide a computer color signal system wherein red, green, and blue video signals are separately fed to three conductors at the input of a multi-conductor cable and wherein transmitter and receiver circuitry readily enables either like phase or relatively reverse phased signals to be transmitted and selectively processed by a receiver without major changes in circuitry.